LIGO -- Studying the Fabric of the Universe
LIGO-GOxxxx
Barry C. BarishNational Science BoardLIGO Livingston, LA4-Feb-04
17-Feb-03 AAAS Annual Meeting 2
A Conceptual Problem is solved !
Newton’s Theory“instantaneous action at a
distance”
Einstein’s Theoryinformation carried
by gravitational radiation at the speed of light
G= 8
17-Feb-03 AAAS Annual Meeting 3
General Relativity
Einstein theorized that smaller masses travel toward larger masses, not because they are "attracted" by a mysterious force, but because the smaller objects travel through space that is warped by the larger object
Imagine space as a stretched rubber sheet.
A mass on the surface will cause a deformation.
Another mass dropped onto the sheet will roll toward that mass.
17-Feb-03 AAAS Annual Meeting 4
Einstein’s Theory of Gravitation
a necessary consequence of Special Relativity with its finite speed for information transfer
gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage
at the speed of light gravitational radiation
binary inspiral of
compact objects
17-Feb-03 AAAS Annual Meeting 5
Detecting Gravitational Waves
Detectors in space
LISA
Gravitational Wave Astrophysical Source
Terrestrial detectors
Virgo, LIGO, TAMA, GEOAIGO
17-Feb-03 AAAS Annual Meeting 6
Frequency range for EM astronomy
Electromagnetic waves over ~16 orders of magnitude Ultra Low Frequency radio waves to
high energy gamma rays
17-Feb-03 AAAS Annual Meeting 7
Frequency range of GW Astronomy
Gravitational waves over ~8 orders of magnitude Terrestrial + space detectors
Audio band
Space Terrestrial
17-Feb-03 AAAS Annual Meeting 8
Detecting a passing wave ….
Free masses
17-Feb-03 AAAS Annual Meeting 9
Detecting a passing wave ….
Interferometer
17-Feb-03 AAAS Annual Meeting 10
Interferometer Concept Laser used to measure
relative lengths of two orthogonal arms
As a wave passes, the arm lengths change in different ways….
…causing the interference pattern
to change at the photodiode
Arms in LIGO are 4km Measure difference in
length to one part in 1021 or 10-18 meters
SuspendedMasses
17-Feb-03 AAAS Annual Meeting 11
Simultaneous DetectionLIGO
3002 km
(L/c = 10 ms)
Hanford Observatory
Caltech
LivingstonObservatory
MIT
17-Feb-03 AAAS Annual Meeting 12
Gravitational Wave Astronomy
LIGO will provide a new way to view the dynamics of the
Universe